Systems and Methods for High Dynamic Range Imaging Using Array Cameras

ABSTRACT

Systems and methods for high dynamic range imaging using array cameras in accordance with embodiments of the invention are disclosed. In one embodiment of the invention, a method of generating a high dynamic range image using an array camera includes defining at least two subsets of active cameras, determining image capture settings for each subset of active cameras, where the image capture settings include at least two exposure settings, configuring the active cameras using the determined image capture settings for each subset, capturing image data using the active cameras, synthesizing an image for each of the at least two subset of active cameras using the captured image data, and generating a high dynamic range image using the synthesized images.

FIELD OF THE INVENTION

The present invention generally relates to digital cameras and morespecifically to systems and methods for high dynamic range (HDR)imagining using array cameras.

BACKGROUND

Current camera technology typically limits image capture possibilitiesto very specific conditions in which an image of acceptable quality canbe produced. As a result of this limitation, several camera settingsneed to be appropriately chosen before an image of optimal quality canbe taken. Cameras have long had the ability to assess the sceneconditions and automatically adjust settings such as: exposure time,iris/lens aperture, focus, sensor gain, and the use of neutral densityfilters. While film-based cameras have traditionally relied on externalmeasuring sensors to select these settings, modern compact digitalcameras make use of several through-the-lens measurements that provideimage-based data to automatically adjust settings through algorithmsthat compare these measurements and decide on optimal settings.

The mechanism of exposure provides adjustment of the device sensitivityto the light intensity in the scene. This is in part motivated by thelimited dynamic range (ratio of highest to lowest light intensity) ofthe camera system compared to the dynamic range of intensities in thereal world. In an imaging capture device, a metering and auto-exposurealgorithm finds optimal values for the above parameters (some of theseparameters may be specified or fixed). An auto-exposure algorithm aimsto find the optimal exposure settings for the camera system by modifyinga subset of the following parameters: exposure time, iris/lens aperture,sensor gain, and the use of neutral density filters.

Cameras equipped with auto-focus lens can generally capture an image ofacceptable quality at a certain focus setting, while relying on anauto-focus algorithm to select the accurate focus position where thechosen parts of the image are considered to be acceptably sharp. In atraditional compact digital camera, auto-focus can be achieved bycapturing successive images (or selected regions of interest insuccessive images) at varying focus positions through “focus sweep” andselecting the setting corresponding to the image (or selected regions ofinterest in the image) of best “focus”. An auto-focus algorithm aims tofind the optimal focus setting for the camera system. The auto-exposureand auto-focus functions in digital cameras share the characteristicthat they both generally rely on taking multiple measurements in orderto estimate the best camera settings prior to actual image capture.

Auto-exposure algorithms may rely on external light meters/sensors ormay evaluate optimal exposure time through the lens by successive imagecapturing as described above. In many legacy cameras auto-exposurealgorithms run concurrently with image preview mode. Due to the factthat preview mode provides real time video, the auto-exposure algorithmis typically configured to make small adjustments in the exposure timesince changes in exposure are immediately visible in the preview video.These small adjustments result in delays in identifying optimal exposuretimes.

Autofocus is another feature that generally runs when the device is inpreview mode. Again, since image preview mode provides real time video,the autofocus process typically involves gradually varying the focuspoint in a slow sweep. Although there are multiple approaches toperforming autofocus (including phase detection that uses dedicatedfocusing sensors), methods appropriate for compact cameras typicallyinvolve capturing several images and analyzing the captured images forparameters such as contrast or blur amount. Such autofocus methods,along with slow sweep, can also result in delays.

The High Dynamic Range (HDR) feature provides a means to produce imagesthat convey higher dynamic range (higher ratio of intensitiescorresponding to light and dark areas in image). In a conventional imagecapture mode (i.e. one that does not involve capturing HDR information),images are traditionally captured at one exposure level (may vary foreach color channel in architectures allowing this). The camera system'sdynamic range is typically limited by several factors, including thefinite number of bits in the analog-to-digital converters, reducedfull-well sensor capacity as well as optical characteristics. HDR modeutilizes a set of methods that sample a scene's dynamic range moreaggressively by capturing multiple images of the scene at differentexposure levels. Each exposure creates brackets of smaller or regulardynamic range that can be sampled to produce a composite image of high(increased) dynamic range. Various blending models and/or algorithms canbe utilized to create a single HDR image from the multiple images. TheHigh Dynamic Range mode typically includes two steps: High Dynamic Rangecapture and High Dynamic Range Image Blending and Compression. In theHigh Dynamic Range capture step, multiple images may be captured at apre-defined difference in exposure setting from the reference exposure;for example, if the reference exposure is EV0, an image with a smallerexposure by a factor of 2 may be captured and an image with a greaterexposure by a factor of 2 may be captured as following: EV0, EV-1 (shortexposure), EV+1 (long exposure). (Note: numbers follow the exposurevalue convention and correspond to base-2 logarithmic scale such thatEV-1 corresponds to half of EV0 exposure, EV+1 corresponds to double theEV0 exposure).

SUMMARY OF THE INVENTION

Systems and methods for high dynamic range imaging using array camerasin accordance with embodiments of the invention are disclosed. In oneembodiment of the invention, a method of generating a high dynamic rangeimage using an array camera includes defining at least two subsets ofactive cameras, determining image capture settings for each subset ofactive cameras, where the image capture settings include at least twoexposure settings, configuring the active cameras using the determinedimage capture settings for each subset, capturing image data using theactive cameras, synthesizing an image for each of the at least twosubset of active cameras using the captured image data, and generating ahigh dynamic range image using the synthesized images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an array camera in accordance with anembodiment of the invention.

FIG. 2 conceptually illustrates an optic array and an imager array in anarray camera module in accordance with an embodiment of the invention.

FIG. 3 is an architecture diagram of an imager array in accordance withan embodiment of the invention.

FIG. 4 is a high level circuit diagram of pixel control and readoutcircuitry for a plurality of focal planes in an imager array inaccordance with an embodiment of the invention.

FIG. 5 is a chart that conceptually illustrates the manner in whichcapturing image data with specific image capture settings can result inthe capture of a portion of the full dynamic range of a scene.

FIG. 6 is a flow chart illustrating a process for performing HDR imagecapture utilizing subsets of active cameras of an array camera module inaccordance with an embodiment of the invention.

FIG. 7 conceptually illustrates a layout of color filters and thelocation of reference cameras within each subset of a 4×4 camera modulein accordance with an embodiment of the invention.

FIG. 8 conceptually illustrates a layout of color filters and thelocation of reference cameras within each subset of a 4×4 camera modulein accordance with an embodiment of the invention.

FIG. 9 conceptually illustrates a layout of color filters and thelocation of reference cameras within each subset of a 5×5 camera modulein accordance with an embodiment of the invention.

FIG. 10 is a flow chart illustrating a process for determining variousHDR image capture modes using a subset of active cameras in accordancewith an embodiment of the invention.

FIGS. 11A-E conceptually illustrate applying various neutral densityfilters for One-shot HDR Mode in accordance with an embodiment of theinvention.

DETAILED DISCLOSURE OF THE INVENTION

Turning now to the drawings, systems and methods for high dynamic range(HDR) image capture using array cameras are disclosed. Array camerasincluding camera modules that can be utilized to capture image data fromdifferent viewpoints are disclosed in U.S. patent application Ser. No.12/935,504, entitled “Capturing and Processing of Images usingMonolithic Camera Array with Heteregeneous Images”, filed May 20, 2009,the disclosure of which is incorporated by reference herein in itsentirety. In several embodiments of the invention, HDR image capture isperformed by grouping subsets of active cameras in an array cameramodule and configuring the cameras within each subset using differentimage capture settings so that multiple images with different exposuresettings can be synthesized using the captured image data and compositedto form an HDR image. The exposure settings can be determined in amanner well known to one of ordinary skill in the art including (but notlimited to) using exposure bracketing techniques. In severalembodiments, one subset is configured to capture image data at lowexposure levels and another subset is configured to capture image dataat high exposure levels. In a number of embodiments, a so called SingleFrame HDR mode and/or Multiple Frame HDR mode can be utilized togenerate an HDR image based upon the depth of objects within the scene.The HDR image capture mode can be selected automatically or manually. InSingle Frame HDR mode, subsets of cameras are configured using variousexposure settings to capture image data over the entire dynamic range ofthe scene (or meaningful portion of the scene's dynamic range) in themanner discussed above. In Multiple Frame HDR mode the same set ofactive cameras is used to capture successive image data using differentcapture settings similar to traditional HDR imagining. In both theSingle Frame and Multiple Frame HDR modes, the captured image data areused to synthesize high resolution images that can be composited tocreate an HDR image. In various embodiments, a gain-based HDR imagingmode can be utilized for various gain settings using methods including(but not limited to) those disclosed in U.S. patent application Ser. No.13/761,040, entitled, “Systems and Methods for Extending Dynamic Rangeof Imager Array by Controlling Pixel Analog Gain”, filed Feb. 6, 2013,the disclosure of which is incorporated by reference herein in itsentirety. In many embodiments, a so-called One-shot HDR mode can beutilized to achieve exposure variation among exposure pattern groups byvarying transmittance while maintaining similar exposure parameters (andspecific integration times) for all cameras within a specific colorchannel in the array. Systems and methods for performing HDR imagecapture in accordance with embodiments of the invention are discussedfurther below.

Array Cameras

Array cameras in accordance with embodiments of the invention caninclude a camera module and a processor. An array camera in accordancewith an embodiment of the invention is illustrated in FIG. 1. The arraycamera 100 includes a camera module 102 with an array of individualcameras 104 where an array of individual cameras refers to a pluralityof cameras in a particular arrangement, such as (but not limited to) thesquare arrangement utilized in the illustrated embodiment. The cameramodule 102 is connected to the processor 106 and the processor 106 isconnected to a memory 108. Although a specific array camera isillustrated in FIG. 1, any of a variety of different array cameraconfigurations can be utilized in accordance with many differentembodiments of the invention.

Array Camera Modules

Camera modules in accordance with embodiments of the invention can beconstructed from an imager array and an optic array. A camera module inaccordance with an embodiment of the invention is illustrated in FIG. 2.The camera module 200 includes an imager array 230 including an array offocal planes 240 along with a corresponding optic array 210 including anarray of lens stacks 220. Within the array of lens stacks, each lensstack 220 creates an optical channel that forms an image of the scene onan array of light sensitive pixels within a corresponding focal plane240. Each pairing of a lens stack 220 and focal plane 240 forms a singlecamera 104 within the camera module. Each pixel within a focal plane 240of a camera 104 generates image data that can be sent from the camera104 to the processor 108. In many embodiments, the lens stack withineach optical channel is configured so that pixels of each focal plane240 sample the same object space or region within the scene. In severalembodiments, the lens stacks are configured so that the pixels thatsample the same object space do so with sub-pixel offsets to providesampling diversity that can be utilized to recover increased resolutionthrough the use of super-resolution processes.

In several embodiments, color filters in individual cameras can be usedto pattern the camera module with π filter groups as further discussedin U.S. Provisional Patent Application No. 61/641,165 entitled “CameraModules Patterned with pi Filter Groups” filed May 1, 2012, thedisclosure of which is incorporated by reference herein in its entirety.These cameras can be used to capture data with respect to differentcolors, or a specific portion of the spectrum. In contrast to applyingcolor filters to the pixels of the camera, color filters in manyembodiments of the invention are included in the lens stack. Forexample, a green color camera can include a lens stack with a greenlight filter that allows green light to pass through the opticalchannel. In many embodiments, the pixels in each focal plane are thesame and the light information captured by the pixels is differentiatedby the color filters in the corresponding lens stack for each filterplane. Although a specific construction of a camera module with an opticarray including color filters in the lens stacks is described above,camera modules including π filter groups can be implemented in a varietyof ways including (but not limited to) by applying color filters to thepixels of the focal planes of the camera module similar to the manner inwhich color filters are applied to the pixels of a conventional colorcamera. In several embodiments, at least one of the cameras in thecamera module can include uniform color filters applied to the pixels inits focal plane. In many embodiments, a Bayer filter pattern is appliedto the pixels of one of the cameras in a camera module. In a number ofembodiments, camera modules are constructed in which color filters areutilized in both the lens stacks and on the pixels of the imager array.

In several embodiments, an array camera generates image data frommultiple focal planes and uses a processor to synthesize one or moreimages of a scene. In certain embodiments, the image data captured by asingle focal plane in the sensor array can constitute a low resolutionimage (the term low resolution here is used only to contrast with higherresolution images), which the processor can use in combination withother low resolution image data captured by the camera module toconstruct a higher resolution image through Super Resolution processing.In many embodiments, the image capture settings of the cameras in thearray are varied to capture image data with different dynamic rangesthat can be composited to form high dynamic range images.

Although specific array cameras are discussed above, many differentarray cameras are capable of utilizing π filter groups in accordancewith embodiments of the invention. Imager arrays in accordance withembodiments of the invention are discussed further below.

Imager Arrays

An imager array in which the image capture settings of a plurality offocal planes can be independently configured in accordance with anembodiment of the invention is illustrated in FIG. 3. The imager array300 includes a focal plane array core 302 that includes an array offocal planes 304 and all analog signal processing, pixel level controllogic, signaling, and analog-to-digital conversion (ADC) circuitry. Theimager array also includes focal plane timing and control circuitry 306that is responsible for controlling the capture of image informationusing the pixels. In a number of embodiments, the focal plane timing andcontrol circuitry utilizes reset and read-out signals to control theintegration time of the pixels. In other embodiments, any of a varietyof techniques can be utilized to control integration time of pixelsand/or to capture image information using pixels. In many embodiments,the focal plane timing and control circuitry 306 provides flexibility ofimage information capture control, which enables features including (butnot limited to) high dynamic range imaging, high speed video, andelectronic image stabilization. In various embodiments, the imager arrayincludes power management and bias generation circuitry 308. The powermanagement and bias generation circuitry 308 provides current andvoltage references to analog circuitry such as the reference voltagesagainst which an ADC would measure the signal to be converted against.In many embodiments, the power management and bias circuitry alsoincludes logic that turns off the current/voltage references to certaincircuits when they are not in use for power saving reasons. In severalembodiments, the imager array includes dark current and fixed pattern(FPN) correction circuitry 310 that increases the consistency of theblack level of the image data captured by the imager array and canreduce the appearance of row temporal noise and column fixed patternnoise. In several embodiments, each focal plane includes referencepixels for the purpose of calibrating the dark current and FPN of thefocal plane and the control circuitry can keep the reference pixelsactive when the rest of the pixels of the focal plane are powered downin order to increase the speed with which the imager array can bepowered up by reducing the need for calibration of dark current and FPN.

In many embodiments, a single self-contained chip imager includes focalplane framing circuitry 312 that packages the data captured from thefocal planes into a container file and can prepare the captured imagedata for transmission. In several embodiments, the focal plane framingcircuitry includes information identifying the focal plane and/or groupof pixels from which the captured image data originated. In a number ofembodiments, the imager array also includes an interface fortransmission of captured image data to external devices. In theillustrated embodiment, the interface is a MIPI CSI 2 output interface(as specified by the non-profit MIPI Alliance, Inc.) supporting fourlanes that can support read-out of video at 30 fps from the imager arrayand incorporating data output interface circuitry 314, interface controlcircuitry 316 and interface input circuitry 318. Typically, thebandwidth of each lane is optimized for the total number of pixels inthe imager array and the desired frame rate. The use of variousinterfaces including the MIPI CSI 2 interface to transmit image datacaptured by an array of imagers within an imager array to an externaldevice in accordance with embodiments of the invention is described inU.S. Pat. No. 8,305,456, entitled “Systems and Methods for TransmittingArray Camera Data”, issued Nov. 6, 2012, the disclosure of which isincorporated by reference herein in its entirety.

Although specific components of an imager array architecture arediscussed above with respect to FIG. 3, any of a variety of imagerarrays can be constructed in accordance with embodiments of theinvention that enable the capture of images of a scene at a plurality offocal planes in accordance with embodiments of the invention.Independent focal plane control that can be included in imager arrays inaccordance with embodiments of the invention are discussed furtherbelow.

Independent Focal Plane Control

Imager arrays in accordance with embodiments of the invention caninclude an array of focal planes that can independently be controlled.In this way, the image capture settings for each focal plane in animager array can be configured differently. As is discussed furtherbelow, the ability to configure active focal planes using differenceimage capture settings can enable different cameras within an arraycamera module to capture image data at various exposure levels forcreating high resolution images that can be composited to create HDRimages.

An imager array including independent control of image capture settingsand independent control of pixel readout in an array of focal planes inaccordance with an embodiment of the invention is illustrated in FIG. 4.The imager array 400 includes a plurality of focal planes or pixelsub-arrays 402. Control circuitry 403, 404 provides independent controlof the exposure timing and amplification gain applied to the individualpixels within each focal plane. Each focal plane 402 includesindependent row timing circuitry 406, 408, and independent columnreadout circuitry 410, 412. In operation, the control circuitry 403, 404determines the image capture settings of the pixels in each of theactive focal planes 402. The row timing circuitry 406, 408 and thecolumn readout circuitry 410, 412 are responsible for reading out imagedata from each of the pixels in the active focal planes. The image dataread from the focal planes is then formatted for output using an outputand control interface 416.

Although specific imager array configurations are discussed above withreference to FIG. 4, any of a variety of imager array configurationsincluding independent and/or related focal plane control can be utilizedin accordance with embodiments of the invention including those outlinedin U.S. patent application Ser. No. 13/106,797, entitled “Architecturesfor Imager Arrays and Array Cameras”, filed May 12, 2011, the disclosureof which is incorporated by reference herein in its entirety. Processesfor capturing HDR image data using array cameras are further discussedbelow.

Capturing Image Data Using Single Frame HDR Mode

The dynamic range of a scene can be used to determine whether HDRimaging is appropriate. A scene's dynamic range can be measured usingmethods including (but not limited to) those disclosed in U.S.Provisional Patent Application Ser. No. 61/775,395, entitled, “Systemsand Methods for Measuring Scene Information while Capture Image Data”,filed Mar. 8, 2013, the disclosure of which is incorporated by referenceherein in its entirety. Many times, the dynamic range of a camera modulecan capture the entire dynamic range of the scene and/or a portion ofthe dynamic range determined to be useful. In such situations, astandard capture mode (non HDR mode) where the same image capturesettings can be utilized for the cameras in each color channel can beused to capture the full dynamic range of the scene. However, asillustrated in FIG. 5, the dynamic range of a scene 502 can be muchgreater than the dynamic range of a single camera in an array cameramodule 506. The difference in dynamic ranges creates a so calledclipping affect at the outer limits of the camera's dynamic range 504,508. The regions of the scene's dynamic range that are outside thecamera module's dynamic range 506 are either underexposed or overexposedand thus image data is not accurately captured. Exposure times can beadjusted at multiple iterations to identify the exposure settings thatbest satisfy a set of predetermined criteria and/or to capture imagedata over the entire dynamic range of the scene for the purposes of HDRimaging. In various embodiments, optimal exposure settings may bedetermined using an iterative process. Processes for performing HDRimage capture using subsets of active cameras within an array cameramodule in accordance with embodiments of the invention are discussedfurther below.

A process for performing HDR image capture utilizing subsets of activecameras within an array camera module in accordance with an embodimentof the invention is illustrated in FIG. 6. The process 600 includescapturing (602) image data using the active cameras of the camera moduleas discussed above. The captured image data can be analyzed to determine(604) the dynamic range of the scene. In order to decide whether toutilize the so called Single Frame HDR mode to capture image data usingsubsets of cameras configured at various settings, a determination (606)is made as to whether the dynamic range in the scene exceeds apredetermined threshold. In many embodiments of the invention, thethreshold can be a function of the dynamic range of the camera moduleimplemented in the imager array. If the dynamic range in the scene doesnot exceed the predetermined threshold value, a standard capture mode(non-HDR mode) is utilized to capture image data where the cameras ineach color channel use the same image capture settings (616) and animage is synthesized (618) using the captured image data. If the dynamicrange of the scene exceeds the threshold value, subsets of activecameras of a camera module can be determined (608) for use in HDR imagecapture as further described below. In various embodiments, the exposuresettings can be determined in a manner well known to one of ordinaryskill in the art including (but not limited to) selecting (610) dynamicrange bracketing for the purpose of high dynamic range capture. For eachsubset of cameras, various exposure settings are determined (612) forcapturing HDR image data. The exposure settings are used to configure(614) each subset of cameras of the camera module to capture image dataat various exposure levels. The active cameras of each subset of camerascapture (616) image data at their respect exposure settings and an imagecan be synthesized (618) for each subset from the captured image data.

Although specific processes for performing HDR image capture usingsubsets of active cameras are discussed above with respect to FIG. 6,any of a variety of processes for performing HDR image capture usingsubsets of active cameras can be utilized as appropriate to therequirements of a specific application in accordance with embodiments ofthe invention. Capturing image data using subsets of active cameras forHDR image capture in accordance with embodiments of the invention arediscussed further below.

Selecting Subsets of Active Cameras for use in HDR Image Capture

Active cameras in an array camera module in accordance with embodimentsof the invention can be arranged into subsets and configured usingvarious exposure settings to capture HDR image data that can be utilizedto synthesize images. The ability to synthesize images can be enhancedby the selection of cameras in each subset. In many embodiments, thesubsets are defined so that red (R) and blue (B) color information aresymmetrically disposed about the green reference camera. Thus in a 2dimensional array the red and blue color information should be availableabove, and below and left, and right of a green (G) reference camera,while in a linear array the red and blue color information is availableto the left and right of the green reference color. In some embodiments,one could also have near-IR spectral color symmetrically disposed aroundthe green reference camera. A camera module including a first subset ofactive cameras and a second set of active cameras configured to captureimage data at various exposure levels in accordance with embodiments ofthe invention is illustrated in FIG. 7. The 4×4 array camera module 700includes a first subset 702 of 8 active cameras including a green cameraat the top left, top right, and bottom left corners, a green referencecamera indicated by a box 704, blue cameras above and below thereference camera, and red cameras to the left and right sides of thereference camera. In several embodiments, the locations of the red andblue cameras within the first subset 702 are swapped and/or analternative collection of cameras can be utilized. The array cameramodule 700 includes a second subset 706 of 8 active cameras including arow of blue, green, and red cameras placed below the first subset 702and a column of red, green, and blue cameras placed to the right side ofthe first subset with a green camera connecting the row and the columnand a green reference camera indicated by a box 708.

Depending on factors including (but not limited to) object location andlight intensities within a scene, various arrangements of active camerasof a camera module into subsets can be determined. A camera moduleincluding a first subset of active cameras and a second subset of activecameras configured to capture image data at various exposure levels inaccordance with embodiments of the invention is illustrated in FIG. 8.The 4×4 array camera module 800 is camera module 700 (FIG. 7) reflectedalong a diagonal axis and includes a first subset 802 of 8 activecameras including a green reference camera indicated by a box 804, agreen camera at the top left corner with a row of red, green, and bluecameras to the right and a column of blue, green, and red cameras below.The camera module 800 includes a second subset 806 of 8 active camerasincluding a green camera at the bottom right, bottom left, and top rightcorners, a green reference camera indicated by a box 808, and redcameras above and below the reference camera, and blue cameras to theright and left of the reference camera. In several embodiments, thelocations of the red and blue cameras within the subset 806 are swappedand/or an alternative collection of cameras can be utilized. In someembodiments, a subset of active cameras is configured to capture imagedata in conjunction with a flash that is triggered to illuminate thescene. The flash could have a spectral profile that is in the visiblerange of wavelengths for cameras in the subset that are sensitive tovisible light. In other embodiments, the flash could have a spectralprofile in the near-IR range for cameras that are near-IR sensitive.

As discussed above, various arrangements and collections of activecameras can be utilized in any of a variety of different array cameramodules including array camera modules having any of a variety of numberand/or arrangement of cameras in accordance with embodiments of theinvention. A 5×5 array camera module including a first subset of activecameras and a second subset of active cameras, where each subset isconfigured to capture image data at various exposure levels inaccordance with embodiments of the invention is illustrated in FIG. 9.The 5×5 camera module 900 includes a first subset of 13 active camerasdenoted by the color of the camera and subscripted with the number 1902. The first subset includes a top row comprising two green cameraswith one at the center and the other at the far right corner; a secondrow comprising a blue, green, and red cameras positioned adjacent toeach other starting with the blue camera from the far left side; a thirdrow comprising a green center reference camera indicated by a box 904and blue camera directly to the right of the reference camera 904; afourth row comprising a red camera on the far left and a green cameraone position from the far right; and a fifth row comprising a green,blue, green, and red cameras positioned adjacent to each other startingwith the green camera from the far left corner. The camera module 900includes a second subset of 12 active cameras denoted by the color ofthe camera subscripted with the number 2 906. The second subset includesa top row comprising a green camera at the top left corner, a red cameraadjacent and to the right of the green camera, and a blue camera twopositions to the right of the red camera; a second row comprising a redcamera at the far right and a green camera adjacent and to the left thered camera; a third row comprising a green camera to the far left, ablue camera adjacent and to the right of the green camera, and anothergreen camera at the far right; a fourth row comprising a red camerabelow the green reference camera 904, a green camera directly to theleft of it, and a blue camera to the far right; and a fifth rowcomprising a green camera at the far right corner.

Although all of the cameras in the array camera modules illustrated inFIGS. 7, 8, and 9 are shown as capturing image data, in many embodimentsone or more of the cameras within the array camera modules of FIGS. 7,8, and 9 can be idle during image capture to conserve power asappropriate to the requirements of a specific application. Furthermore,the subsets need not contain the same number of cameras. In manyembodiments, the cameras in an array camera module are configured intosubsets having different numbers of cameras in order to perform HDRimage capture.

Although specific arrangements of active cameras into a first, secondand/or third subsets of active cameras of a camera module are discussedabove with respect to FIGS. 7, 8, and 9, various camera module sizes andany of a variety of arrangements of active cameras into subsets ofactive cameras in camera modules can be utilized as appropriate to therequirements of a specific application in accordance with an embodimentof the invention. Processes for capturing image data at various exposurelevels in consideration of objects within the scene are furtherdescribed below.

Capturing Image Data Using Single Frame and/or Multiple Frame HDR Modes

Disparity increases the closer an object is to the cameras in an arraycamera module. When a smaller number of cameras capture image data, thelikelihood that artifacts will be created near depth discontinuities inan image synthesized using the color data is increased due to thepresence of occlusions. The likelihood that such artifacts will bepresent is highest when an object is close to the cameras and thedisparity between the object in the captured images is greatest due tothe fact that occlusion areas are largest. For scenes containing objectsonly at far distances and when using arrays with a limited number ofcameras, single frame HDR mode may be utilized. At these distances, thelikelihood of incurring significant occlusion artifacts is very small.In many embodiments of the invention, if an object within a scene iswithin a predetermined distance from the array camera module, thenMultiple Frame HDR mode is utilized. The Multiple Frame HDR modefunctions similar to traditional HDR imagining, where the same set ofactive cameras is used to capture successive image data using differentcapture settings. The sets of image data are used to synthesize highresolution images that are then composited to create an HDR image. Thebenefit of configuring the active cameras to capture successive set ofimage data using different image capture settings is that more camerascan be utilized relative to the Single Frame HDR mode and the likelihoodof artifacts is reduced. If the object within the scene is a sufficientdistance away, then Single Frame HDR mode can be utilized as describedabove. The threshold distance can be determined based on the cameraarray specification and depends on baseline between furthest cameras,focal length and the sensor pixel pitch using the general stereodisparity formula: disparity [in pixels]=baseline*focallength/(distance*pixel_pitch). In some embodiments, the thresholddistance is computed such that the disparity between these furthestcameras is below 1 pixel such that the potential occlusion artifacts areminimized.

A process for performing HDR image capture using subsets an array camerain a manner that adapts based upon scene object distance in accordancewith an embodiment of the invention is illustrated in FIG. 10. Theprocess 1000 includes capturing image data using one or more activecameras. The image data can be optionally used to synthesize an imageand generate (1002) a preview of the synthesized image. The synthesizedimage and/or captured image data is analyzed to estimate (1004) thedynamic range of the scene. In many embodiments, a determination is made(1006) as to whether the dynamic range of the scene exceeds apredetermined threshold. If the dynamic range of the scene does notexceed the predetermined threshold, HDR imaging is not utilized andimage data is captured using a standard (non-HDR) image capture mode(1016). If the dynamic range in the scene does exceed a threshold value,then a depth map is generated (1008) based upon the preview and/or thecaptured image data. In various embodiments, the depth map can begenerated using methods including (but not limited to) techniquesdisclosed in in U.S. Provisional Patent Application Ser. No. 61/691,666,entitled, “Systems and Methods for Parallax Detection and Correction inImages Captured Using Array Cameras” filed Aug. 21, 2012, the disclosureof which is incorporated by reference herein in its entirety. In severalembodiments, the depth map is evaluated to determine (1010) if an objectis within a predetermined threshold distance from the array cameramodule. If the objects are within the threshold distance, then MultipleFrame HDR imaging mode is utilized (1012) to capture image data asdescribed above. If the objects are not within the threshold distance,then Single Frame HDR imaging mode is utilized (1014) to capture imagedata as described above. In various embodiments, One-shot HDR imagingmode can be utilized to achieve exposure variation among exposurepattern groups of active cameras of an array while maintaining similarexposure parameters for all cameras within a specific color channel inthe array as further discussed below.

Although specific processes for performing HDR imaging using subsets ofactive cameras in consideration of object distance are discussed abovewith respect to FIG. 10, any of a variety of processes for performingHDR imaging using subsets of active cameras in consideration of sceneobject distance can be utilized as appropriate to the requirements of aspecific application in accordance with an embodiment of the invention.Capturing image data using One-shot HDR Mode imaging in accordance withembodiments of the invention are discussed further below.

One-shot (same-exposure) HDR Mode Imaging

As discussed above, HDR imaging can be achieved in an array camera byindependently controlling exposure for various subsets of activecameras. Typically, when a particular subset of cameras are exposeddifferently than the cameras in a main exposure subset, a trade-off ismade between spatial resolution in the main exposure for increaseddynamic range (effectively increasing exposure sampling at the expenseof decreased spatial sampling at the main exposure). However, in somesystems and/or applications, it may be beneficial for all active camerasin the array to share the same exposure parameters (such as but notlimited to systems where super-resolution processes are performed).

In many embodiments, a so-called One-shot HDR mode can be utilized toachieve exposure variation among subsets of active cameras (exposurepattern groups) while maintaining similar exposure parameters (andspecific integration times) for all cameras in the array. Such exposurevariation can be achieved by varying transmittance from one exposurepattern groups to another. The One-shot HDR mode can be implementedutilizing filters including (but not limited to) color and/or neutraldensity filters. In several embodiments, color filters can be stacked orthe thickness of a filter layer varied to allow for desiredtransmittance. In other embodiments, the transmittance of eitherindividual cameras or a camera group may be controlled by an LCD placedin the optical path.

Exposure pattern groups can be determined by selecting a subset ofactive cameras and applying the color and/or neutral density filters tothe subset. In many embodiments, neutral density filters correspondingto the exposure pattern group may be permanently applied in the opticalpath in front of a lens, between different lens elements and/or betweenthe lens and the sensor or even lithographically deposited on the lens,sensor or additional glass carriers. In other embodiments, neutraldensity filters corresponding to desired exposure pattern groups may beinserted, on demand, in the optical path. Further, neutral densityfilters can be part of the camera array module internally and may becontrolled mechanically and/or electronically or attached externally ontop of the camera array module by the user whenever One-shot HDR mode isdesired.

In many embodiments, the neutral density filters can be individualfilters that are applied to each individual active camera or a singlearray filter that can be applied to all cameras of an exposure patterngroup. Conceptual illustrations for applying various neutral densityfilters for desired exposure pattern groups in accordance with anembodiment of the invention is shown in FIGS. 11A-E. Application ofindividual neutral density filters for One-shot HDR mode in accordancewith an embodiment of the invention is shown in FIGS. 11A-B. WhenOne-shot HDR mode is not enabled 1100, the neutral density filters 1104do not cover the optical paths of the lens 1102. However, when One-shotHDR mode is enabled 1110, the neutral density filters are placed in theoptical path 1112. The desired exposure pattern group can be created byplacing one or more individual filters (as indicated by the shadedregions).

In some embodiments, particularly where the desired exposure patterngroup represents cameras clustered close together, a single arrayneutral density filter can be used. Application of an array neutraldensity filter for One-shot HDR mode in accordance with an embodiment ofthe invention is shown in FIG. 11C. When One-shot HDR mode is enabled1120, a single array filter 1122 creates the desired exposure group. Inseveral embodiments, a single neutral density filter can be appliedusing a rotating wheel mechanism. Application of array neutral densityfilters utilizing a rotational mechanism for One-shot HDR mode inaccordance with embodiments of the invention are shown in FIGS. 11D-E.When One-shot HDR mode is enabled 1130, the array filter 1132 covers theoptical paths for the exposure pattern group. When One-shot HDR mode isnot enabled, a rotational mechanism 1134 removes the array filter. Invarious embodiments, the rotational mechanism 1146 can provide forseveral exposure group patterns corresponding to different positionsalong the rotational path. In one position, an array filter 1142 cancover one exposure pattern group. Upon rotation, another filter 1144 cancreate a different exposure pattern group. Further, the rotationalmechanism can also provide for not applying any filter at all. Asdiscussed above, the shape and size of the neural density filters canvary along with the specific method of implementation. Although specificneutral density filters and their application to an array camera forenabling One-shot HDR mode are discussed above with respect to FIGS.11A-E, any of a variety of filters and applications to array cameras asappropriate to the requirements of the a specific application can beutilized in accordance with embodiments of the invention.

While the above description contains many specific embodiments of theinvention, these should not be construed as limitations on the scope ofthe invention, but rather as an example of one embodiment thereof. It istherefore to be understood that the present invention may be practicedotherwise than specifically described, without departing from the scopeand spirit of the present invention. Thus, embodiments of the presentinvention should be considered in all respects as illustrative and notrestrictive.

What is claimed is:
 1. A method of generating a high dynamic range imageusing an array camera, the method comprising: defining at least twosubsets of active cameras; determining image capture settings for eachsubset of active cameras, where the image capture settings include atleast two exposure settings; configuring the active cameras using thedetermined image capture settings for each subset; capturing image datausing the active cameras; synthesizing an image for each of the at leasttwo subset of active cameras using the captured image data; andgenerating a high dynamic range image using the synthesized images.